Flue gas sampling system



March 29, 1960 G. D. FowLE, JR.. EVAL 2,930,237

FLUE GAs SAMPLING SYSTEM I5 Sheets-Sheet 1 Filed June 19. 1956 March 29,1960 G, D, |ow| El JR., ETAL 2,930,237

FLUE GAS SAMPLING SYSTEM 3 Sheets-Sheet 2 Filed June 19, 1956 March 29,1960 s. D. FowLE, JR ETAL 2,930,237

FLUE GAS SAMPLING SYSTEM 5 Sheets-Sheet 3 Filed June 19, 1956 umm I, mp

ONl!

Yitecl States,

z,93,o,z3,1 FLUE GAS SAMPLING SYSTEM George D. Fowle, Jr., Ithan, andHarry A. Kraftson, Bala-Cynwyd, j Pa., assignors lto VLeeds and NorthrupCompany, Philadelphia, lla., a corporation :of Pennsyh vanta Application.lune 19, 1956, Serial No.459275413 lzclaims. (ci. 7er-421.5)

arent f the invention; t

ploblemzhasbeenlfurther complicated by .reason of'the fact that lineducts themselves `are sometimes 'subdivided in regulation ...ofgtheViiolw tof Vcombustion products through onefvorinloremonomizersfor other-'types of 'heat exchange units. 'The'iprohlemmpartzis oneof'stratification ofthe gas streamicausel by;incomplete.mixing ofthegases ibeforopssing into :the stack. Where the ueigas duct extends:across the -steam tboiler Awhich `is lired from a f plurality ofyburners, :the stratification problem is aggravated since uniformity ofgas composition in the ue duct'fwill then depend upon :aplurality offactors; 'including' Athe uniform and equal-rates fof supply of fuel andair'tothe several fburners.

It is frequently 1desirablefto take gas -samples :from vthe ue gasductwork fromgaposition `upstream fromthe air preheater, and :at ithispoint the ductwork :may fhave -a v eross-sectionhaving dimensions `of30-or 40 feet by 15 0r 2O feet. With Ycross-sectional 'areas for theIiiowpathof this Aorder invmind, Va lbetter understanding Will be'had ofthe problem of stratification.

Recirculation means and ,dampersinthe gas passages which :form va fpartof ,the heat control 1system1for the boiler further .complicate thestratification problemas lit affects the -obtainment of :gas-samplesxwhichare truly representative of the flue gas constituents.:These constituents are .increasingly important :as .a guide to `theamount of Yexcess I-air :in Athe `furnace propen'particularly forfurnaces having recirculating'ue gases. 1n ,accordance with the presentinvention, Ia `plurality of flue gassamplesare withdrawn from vselected`regions of A.the ue gas 4ductwork andare so located with respect to thegas ductwork 1and the Vfactors lwhich affect flue gas ilow therein thatan average-thereof can be utilized as Arepresentative-oi the flue gasWithin the duct. `These gas samples are preferably obtained inaccordance with the method and apparatus of copending application SerialNo. l558,731,` filed January 12, 1956 by AHarry A. yKraftson, yet al.,issued `July 21, 11959 as United lStatesgLetters Patent No. 2,895,335.Each j'ilue :gas sample is cleaned tovprovidealiquid-free.and;solidfree-.gas sample. 'I he arrangement disclosed in@said copending 'application iassures continuity of Vgas liow from eachof the 'selected locations of theductworkA and contributessto thereliability of operationof embodiments of the present invention.

The clean gas samples -are directed to flowchannels, each ofwhichincludes a flow-meter andgaowradjusting orifice. There. is providedameans commento eachjiow passage :for lmaintaining a .constant backpressure upon the ow meters. =Each said orifice in the form of a ow- A,2,930,237; rarement .Mart 129,.'1960 l.adjusting valve is fthenregulated fto provide .a -known ,and Y'predetermined flow rate foreachgas fsample., The selected .gas samples `are fthen mixed :together inorder to-provide a weighted average :gas sample which will be trulyrepresentativo of the gases passing through the ductwork.

:For Vfurther objects and advantages ofthe invention and .for a detaileddescriptionof typical embodiments thereof, :reference is .to be had'tozthe following description taken `in conjunction with :theaccompanying'draw ings, 2in which:

Fig. l ,diagrammatically illustrates oneLenibo'clir'nentof fig. 2illustrateszalseparator of the type which maybe .used in each embodimentof the invention;

-Fig. ,3 diagrammatically illustrates a cleaning and scrubbingarrangement applicable tofeach embodiment of the invention; and f Fig. 4diagrammatically illustrates a modified form of theinvention. e Y vReferring to Fig. 1, 'the invention in one 1formhas Abeen shown appliedto a line gas lduct 10 which, itwill b,eg.'observed,-has a largecross-sectional area-normal -to the path vof yiow' and through which-flue gases, may

stratify, making diiiicult the obtainment of avgas, sampley whosecomposition isrepresentativ'e of thefreal average Composition of thegasystream within theduet Y10, In accordance with ythe invention, ythereare lnot lo'nl,y`-pro videdaj'plurality of :gas-.probes 1.1, 12 land 13Jdisposed atditferent locations across the duct 110,but there are alsoprovided means =for2delivering to 'a mixing-zone or averaging manifoldvsubstreanlswliich dow by way of pipes M, 1S and 16, A`each 'having' a"ow rate vwhiclrgis main- Y tainedinelixed'relation to the owzrates ofthe remaining substreams.` Y

As will :later be more fully explained, `the lprobes 1f1-13 `are:preferably of :the rtype fdiselosed -in said-copending application"Serial No.v 51583731 -and include a' selfeicleani'ng feature for theend tof eachkvprobe which minimizes clogging and whichmaintains'substantially uniform :the :withdrawal Vof. sampling streamsfrom :the Aduct Y 1t); .The arrangement -of said applicationlalsoincludes anjnjector 17 'and a scrubbing arrangement which `in:conjunction with a separator-18 'delivers -into ajpipe v19 4:5l

a solid-free and liquid-free stream of iluemgas. In uaccordancewithithepresent inventiomthe cleanfgas stream is idelivered to fa furtherseparator 20 having associated therewith l`a Aback pressure rregulatingdevice21. 'The separator 2t)V is fconnected to aiiow meter 22 andjncon?junction with a throttling valve 23 uprovides fa metered flowof ya cleansubstream of 'due gas -in .the lpipe i14. Likeiprovisions havebeen madefor theremaining probes 12 and 13 and corresponding parts have beengiven'like reference characters, but `with the addition offsu'ixes 4aand b. Y Y

.The back pressure `regulating means21 includes ajpipe 24-extending'from 'the separator 20 to la subsurfaceflevel which provides a head orApressure against which the vgas from yseparator 20 must ow. Moreparticularly, the v clean :sampling `stream in pipe 19 is undersubstantial` pressure .and it flows at a -reiatively highfrate'into theseparator 20. tlnjoughxthel z pipe "19 is adjacent 'a ywall thereof andjproduces Awithin the-separator 20 rotation "o 'f'the gases. Anydroplets of moisture present, due tocondensationofwater vapor, willVthereby be thrown to the Wallsof vthe sepa@ rator by kway ofameter '22and'throttling valve ,23, f

the pipe 14, a mixing :zone for manifold v25, and a gas analyzing means26. A waste stream ows from the As better shown in `Fig.f2, Vits entry 3separator 20 by way of the line 24 and through the liquid 21w of thedevice 21.

The tlow meter 22 may be of any suitable type and has been illustratedas a rotameter which includes a oat 27 which, by reason of a tapered owchannel, rises and falls relative to a scale to indicate ow rate.Accordingly, by adjusting the throttling valve 23, a particular ow ratemay be selected as indicated by the flow meter 22. Thereafter, change inthe rate of flow of the clean sampling stream in pipe 19 will not affectto any substantially degree the ow rate in the pipe 14. This desirableresult is accomplished by reason of the constant back pressure which ismaintained upon the dividing means or separator 20 by the fixed backpressure due to the fixed level of liquid 21W in the device 21. Thus, asthe How rate of the clean sampling stream 19 changes, the ow rate of thewaste j stream through the pipe 24 changes to maintain a substan- Ytially constant back pressure upon the meter 22 and particularly uponthe entrance side of the throttling valve 23. Thus, there is maintaineda substantially constant differential of pressure between the dividingmeans 20 and the analyzing means 26 and particularly at the manifold 25.The analyzer 26 is provided with a gas outlet 26a, and each of theconstant back pressure devices 21, 21a and 2lb is provided both with gasoutlets and with constant liquid level devices which, in Fig. 1, havebeenv illustrated as including the piping 29 and 30 interconnecting thevessels and the outlet pipe 31 which discharges into a drain 32.

The throttling valves 23, 23a and 23b will be adjusted to predeterminethe rate of flow of each substream within the pipes or gas flow channels14, and 16. While in general the rates of How of the substreams in pipes15 and 16 will be adjusted to the same rate of ow as the substream inpipe 14, itis to be understood that they may differ one from the other.For example, velocity measurements may be made within the duct 10 todetermine the uniformity of ow of gases at the locations of the probes11-13. Where the rates of flow differ, the throttling valves 23, 23a and23b may be adjusted to provide corresponding differences in ow rates forthe substreams in pipes 14-16 respectively. The particular locationsselected for the probes 11-13, and the number of them, may vary withdifferent installations. In general, they will be of adequate number andso located within the ue duct 10 that the mixture of the streams Withinthe manifold 25 will be representative of a true average composition ofthe gas stream in the duct 10, i.e., a weighted average gas sample.

The throttling valves 23, 23a and 23b represent convenient means forindividually adjusting the rates of flow of the substreams in pipes14-16. The flow rates of the substreams can in the absence of thethrottling valves be adjusted by varying the depth below the liquidlevel of each of the devices 21, 21a and 2lb of the pipes 24, 24a and24b. For example, by decreasing the depth of penetration of the pipe 24in the liquid 21w, a lower rate of gas ow of the substream in pipe 14will be obtained. By having each of pipes 24, 24a and 241; extend intothe liquid to different subsurface levels, further adjustments can bemade in the ow rates of the substreams in pipes 14-16.

The substreams in the mixing zone or manifold 25 thoroughly mix togetherand pass by way of the pipe 33 into the gas analyzing means 26 andoutwardly therefrom through the discharge element 26a.

The analyzing means 26 may be of conventional design; for example, asshown in United States Letters Patent No. 2,603,964 to G. M. Foley etal., and will be selected for the determination of the concentrationwithin the flue gas of the constituent or constituents of interest.These are, in general, the oxygen content, the content of carbondioxide, hydrogen, carbon monoxide, and the like, though 1t is to beunderstood that these examples are to be taken as illustrative and notby way of limitation.

Where cleaning devices of different character are t-utilized or wherethe gas samples to be averaged are initially clean, the dividing means20, a and 20b may suice for removing condensation. For such systems andfor other types of scrubbing devices, suction may be applied to theoutlet 26a and to the outlet 21e to establish the pressure differentialrequired by the system. In this modification, the discharge pipe 31 willbe provided with the usual water seal which may be in the formillustrated in Fig. 4.

Mention has already been made of the fact that each probe and associatedcleaning means is of the type disclosed in said copending applicationSerial No. 558,731. In brief, the probe 11, Fig. 3, includes a pipewithin which there is a water spray 40 directed outwardly of the probeand also toward the walls of the surrounding tube. By action of a steaminjector 41, ue gas is withdrawn into the probe and directed into ascrubbing chamber 42 into which there is introduced a stream of water asthrough the nozzle 43. The steam from the injector 41 is condensed inthe scrubbing chamber 42, and the mixture is directed tangentially intothe separator 18. The mixture within the separator 18 ows in a vorticalpath, and solid material from the line gases is effectively thrown tothe outer walls of the separator and washed downwardly. A float 44actuates a valve 45 to maintain a substantially constant level of liquidwithin the separator 18. A cleaned stream of gas flows outwardly throughthe pipe 19. For a more detailed description of the arrangement, reference may be had to said copending application.

Referring now to Fig. 4, corresponding parts have been given the samereference characters as in the modification of Fig. l. The clean gassamples enter the separators 20, 20a and 20b as by way of the pipes 19,19a and 19b. These separators again function as how-dividing means, butthe manner in which regulated and predetermined rates rof flow areestablished in the lines 14, 15 and 16 differs from the arrangement ofFig. 1. In Fig. 4 the pipes 50, 50a and 50b are drain pipes forcondensate from the separators, and each terminates within a liquidsealing arrangement shown as a vessel 51 of suliicient depth to preventgas flow through the drain pipes 50, 50a and 50h. The back pressure uponeach of separators 20, 20a and 20b is regulated by a back pressureregulating valve 52 which maintains a constant pressure upon a manifold53 which, in turn, is in ow connection with the separators by way of thevalves 54, 55 and 56 and by way of pipes 57, 57a and 57b. Accordingly,the throttling valves 23, 23a and 23b can be adjusted in conjunctionwith thefowmeters 22, 22a and 22b to predetermine the ow rates in thesubstreams owing by way of lines 14, 15 and 16 into the mixing zone ormanifold 25. The back pressure regulating valve 52 in conjunction withthe manifold 53 performs the same function as the devices 21, 21a and2lb of Fig. 1. The arrangement of Fig. 4 will, in general, be preferredby reason of the saving in space and the avoidance of providing a supplyof liquid 21w to maintain constant liquid level in the several backpressure regulating devices 21, 21a and 2lb.

Further in connection with Fig. 4, the valves 54-56 have beenillustrated as three-way, two-position valves, and they provideadditional desirable features of operation in conjunction with the lines58, 58a and 58b. Thus, the valve 56, for example, may occupy a positionVdiffering from that of thevalves 54 and 55 and serve l57b and toprovide a gas passage from the upper end of the ow meter 22b to the backpressure manifold 53.

Accordingly, all of the sampling stream entering through indicate therate of ow of the sampling stream in 19b,

while the flow meters 22 and 22:: will be continuously indicating therates of ow of substreams flowing into l claims.

. A`i1ow o'fsubstreams or fsamplingtstreams.

'It is vhere emphasized thatrthe `valvesfStLSi in either ofi-theirpositions do not 'affect `in any wayrany'o'fthe rates of ow, andparticularly the rates of "ow Jofthe substreams passing` by way ,ofpipes14-16 .into the averaging manifold '25. O perationof valve '56, asdescribed, merely 'changes A-theilowio'f the waste stream from ajpointahead o il the entrance tto fiow meterfZb :to 4'a pointfollowing `the owmeter,- ie., atits foutlet.' Since the back v pressure ,is applied :by.Way 'of thegow :connectionszfor the waste stream, it ,too 'istransferred :as :between inlet to, pipe 57h, to outlet from, pipeV5817., of ow meter ZZb. 1 The additional .iexibility thus provided hasbeen found of considerable vluein many applica- Vtions ofV theinvention. .Forrexampleglit .will be desirable occasionally to check the:probes ,f1-145 Fig. 1, in terms of the ow rates ofilue ,gases withdrawnfromthe ,duct #10. This 1'is readily Vdone by re=routing the samplingstreams 'of pipes 19, "19aand L19b Athrough ,the fow meters 22, 22a and22b. There is thus obtained direct measurement of the flow rate of eachsampling stream without affecting the system as a whole which maintainsconstant the ow rate of the substreams entering the manifold 2S.

Should the `new meter 2211 indicate that there has been a substantialdecrease in the ow rate of the sampling stream through pipe 1%,anindication wil-l be had that something has gone wrong with thatparticular sampling arrangement. if the indicated ilow rate drops belowthat desired in the substream 16, valve 23h will be closed and operationcontinued on the basis of the substreams 14 and 15. Thus, the gasanalyzing means 26 can continue to function until the condition whichadversely affected the ow rate in sampling line 19b has been corrected.This feature is of importance Where the gas analyzer 26 is being reliedupon for control of the combustion conditions within a steam boiler.

The valves 54-56 are 4likewise helpful when placing the system as awhole in operation, since the ow meters 22, 22a and 22h then provide ameans of readily adjusting the flow rates of each of the samplingstreams in pipes 19, 19a and 19h as by the adjustment of the steaminjector 41, a steam valve 41a being illustrated in Fig. 3 for thatpurpose.

Applicable to both systems is a further variation which may be tal/.enas suggestive of additional changes and modifications which will nowsuggest themselves to those skilled in the art and Within the scope ofthe appended and 23b provide for selective sampling across the 'duct 10,Fig. 1, for the purpose of providing information of the concentration ofthe constituent at each probe location. By closing the throttling valves23 and 23a, ue gas will be delivered to the analyzer 26 by Way of thesubstream 16, and the analyzer will indicate the concentration of theselected constituent for the location of the probe 13. By closingthrottling valve 23h and opening throttling valve 23a, the samemeasurement may be made for the location of probe 12. By repeating theforegoing steps, closing valve 23a and opening valve 2.3, there willhave been completed a traverse-survey of the duct l@ with successiveindications of the concentration of the selective constituent at theseveral probe locations. The foregoing can be accomplished in a minimumof time in contrast with the physical movement of the probe from onelocation to another within the duct.

What is claimed is:

1. An apparatus `for obtaining an average gas sample of gas beingsampled, comprising a plurality of sampling probes spaced one from theother for withdrawal of sample gas streams from a plurality of different1oca- More particularly, the throttling valves 23, 23a

spectively receiving said gas. streams yjfor dividing 'ea-ch sample gasstreamY into ja'substream and ajwaste.;streain, a mixing/manifold'fconnected Lto vsaid dividing means vto rreceive saidsubstreams 'meansfor maintaining 'a v,cons tar'l't diierentialofvpressurenp'on {eachsubstream"between said entrance openingsofsaid-dividing means and said mani- 'fold "for establishing a 'owA ratejinto 'said qmanifold of `eaclisubstream, which .ow ratebearsaffixedrelation to the iow rates ot thevremainingsuljlstreamsnotwithstanding wide 'variations in ow rates fofthe sample fgas streams, Aand analyzing-means "tiowfconnected .to'.sa'id manifold for determiningfthe `concentration within the mixtureof the substrearns o'f atfleast one `constituent thereof. y y l nmaintaining saidiconstant diierential fof .pressre Vincludes providedfor each substream, and valve means forV se-Y lectively controlling thegas iiow through each ow meter for measurement of theflow'rate -of thesubstream or the Vflow rate of the sample gas stream.

6. An apparatus for obtaining anaverage gas sample from a flue duct ofextended cross-sectional area, comprising a plurality of sampling probesspaced one from the other across said duct for withdrawal of sample gasstreams from a plurality of different locations, means' f for cleaningliquids andsolids from each sample gas stream, dividing means 'having' aow meter in series now-connection with a first outlet therefrom fordividing each cleaned sample gas stream into a substream and a Wastestream, said dividing means having an inlet for receiving said cleanedgas stream and two outletsy for said waste stream, one in flowconnection with the inlet to said flow meter and the other at thedownstream end of said tlow meter, means including a valve forselectively withdrawing the Waste stream from onerof said two outlets, aback pressure regulating means including a manifold, means includingsaid valves for (selected application ot the back pressure to one ofsaid two outlets for the selected measurement respectively by each saidow meter of each sample gas stream and of veach subream, an averaging 1manifold receiving a substream from each of said dividing means, andanalyzing means How-connected to said averaging manifold vfordetermining the concentration within the mixture ofrthe substreams of atleast one constituent thereof.

7. An apparatus for obtaining an average'gas sample from a plurality ofsample gas streams withdrawn from a duct, comprising dividing meanshaving entrance openings connected respectively to receive each of thesample gas streams for dividing each of said streams into a sub streamand aV waste stream, a mixing and 4averaging manifold receiving thesubstreams, means including a back pressure regulating device formaintaining a constant differential of pressure upon each substreambetween said entrance openings to said dividing means and said manifoldfor establishing a flow rate into said manifold of each substream-*whichbears a fixed relation to the iiow rates of the remaining substreamsnotwithstanding wide variations in now rates of the sample gas streams,and a flow connection to said averaging manifold for withdrawaltherefrom of a weighted average gas sample having a compositionrepresentative of the average composition of the flue gas within saidduct.

8. 'Ihe apparatus of c1airn'7 in which said means for maintaining saidconstant diierential of pressure includes a back pressure regulatingdevice common to each of said dividing means.

9. The apparatus of claim 8 in which said means for maintaining saidconstant dierential of pressure includes a throttling valve for eachsubstream.

10. The apparatus of claim 7 in which each substream has a flow meterfor indicating the rate of ow thereof.

11. The apparatus of claim 7 in which a tiow meter is provided for eachsubstream, and valve means for selectively controlling the gas tiowAthrough each ow meter for measurement of the ow rate of the substream orthe ow rate of the sample gas stream.

12. The method of obtaining a gas sample from a duct of largecross-sectional -area which is representative of the average quality ofthe gas mixture within said duct, which comprises withdrawing sample gasstreams from a plurality of points within the duct, cleaning each samplegas stream of liquids and solids, dividing each clean sample gas streaminto a substream and a waste stream, passing each substream through aflow restriction, increasing and decreasing the rate of ow of each wastestream as the rate of ow of each said sample gas stream increases anddecreases by applying to the inlet side of each ow restriction the samesubstantially constant pressure, whereby the flow rate of each saidsubstreams remains substantially constant notwithstanding widevariations in flow of each sample gas stream and of each waste stream,andrnixing together said substreams in a mixing zone.

References Cited in the tile of this patent UNITED STATES PATENTSChemist-Analyst, volume 14, Jan. 1, 1930, p. 17. (Copy in Div. 36.)

